Ic emi filter with esd protection incorporating lc resonance tanks for rejection enhancement

ABSTRACT

An integrated circuit (IC) electromagnetic interference (EMI) filter with electrostatic discharge (ESD) protection incorporating inductor-capacitor (LC) resonance tanks is disclosed. The filter comprises at least one circuit composed of a diode and an inductor connected in series, wherein the diode induces a parasitic capacitance and the circuit is grounded. When a number of the circuit is two, a passive element is coupled between the two inductors and cooperates with them to induce two parasitic capacitances connected with the circuits. When a number of the circuit is one, two diodes respectively connect with the inductor through two passive elements. Each diode can induce a parasitic capacitance. The two passive elements and the inductor can induce a parasitic capacitance connected with the circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic interference (EMI)filter, particularly to an integrated circuit (IC) EMI filter withelectrostatic discharge (ESD) protection incorporatinginductor-capacitor (LC) resonance tanks for rejection enhancement.

2. Description of the Related Art

Low-pass filter circuit related to this invention is used to blockincoming electromagnetic interferers to wireless communicationelectronic systems, such as a cellular phone. Such a low-pass filtercircuit has several critical specifications (specs) to meet the systemrequirements, including a low pass-band insertion loss (IL), a broadpass-band and high rejection-band attenuation. A low insertion loss forthe filter ensures the desired baseband signals passing through with aslittle energy loss as possible. A broad low pass-band, defined as thefrequency bandwidth from direct-current (DC) to a cut-off frequency(i.e., f_(c)) measured at the 3 dB insertion loss point, allows thedesired baseband signals with wider frequency spectrum (i.e., lots ofuseful baseband harmonic signals) to pass through filter. Typically, awider pass-band (i.e., higher f_(c)) enables higher wirelesscommunication data rates. The rejection-band is determined by thewireless system applications, typically featured from 800 MHz to 6 GHz.The rejection band serves to remove any high-frequency ElectromagneticDisturbance (EMI) interferers, or, noises, which are generallyassociated with the carrier band frequencies in radio-frequency (RF)systems. To ensure the desired data rates and signal integrity, a −30 dBattenuation in the rejection-band for the EMI interferes is preferred inthe EMI filter circuit designs, which means that the noise power must bereduced by a factor of 1000, to ensure the required signal-to-noiseratio (SNR) for the wireless systems. It is well known that a π-shapeCLC type filter 10, shown in FIG. 1( a), can theoretically achieve therequired low-pass filter function described above. Similarly, a π-shapecapacitor-resistor-capacitor (CRC) type LPF circuit 12, as illustratedin FIG. 1( b), can be used to achieve the required filter function. FIG.2 describes the typical filter insertion loss curve, or, called theforward amplification gain (S₂₁) curve characterized in the S-parametermeasurement in practical designs. However, in practical filter designs,to achieve the required low insertion loss and broad pass-band, whileobtaining high rejection-band attenuation, are in conflict and verychallenging, which requires careful filter circuit design trade-off andinnovative design techniques. In particular, the S₂₁ curve should have avery clean −3 dB cut-off frequency (f_(c)) and a fast roll-offattenuation curve, i.e., a steep S₂₁ curvature after the designed f_(c)point. The conventional CLC filter circuit cannot achieve theserequirements due to various integrated circuit (IC) and packageparasitic effects. All prior arts may not satisfactory due to thecircuit performance and the circuit complexity.

FIG. 1( a) shows the ideal CLC LPF filter circuit schematics, which is aclassic third-order filter circuit. The filter circuit can be consideredas a typical 2-port network consisting of the port 1 (input) and theport 2 (output) symmetrically. This basic CLC filter consists of twocapacitors and one inductor to realize the low-pass filter function.FIG. 3 shows a practical CLC LPF filter circuit schematic including theunavoidable parasitic components and integrated ESD protection diodes. Aresistance 14 is the series resistance associated with the conductionchannel inductor 16, which causes the insertion loss due to resistiveloss. Two inductance 18, one inductance 20 and one resistance 22 modelthe parasitic inductance and resistance associated with the bonding andpackage of the filter circuit, respectively. The capacitances 24 canutilize the junction capacitance of the integrated ESD protection diodes26 (or other ESD protection devices). As shown in the filter schematics,any EMI interferers (i.e., noises) can be filtered out in each directionof the 2-port network. In a typical application scenario as illustratedin FIG. 4, the low-pass filter 28 is placed between the baseband IC chip30 and the display 32 (e.g., a liquid crystal display, or LCD) port in aSmartphone printed circuit board (PCB). This filter allows the desiredbaseband signals pass through, while blocking the undesiredhigh-frequency interferers emitted from the noisy LCD module. Some priorarts used fifth-order LC filter circuit and coupled inductors to enhancethe filter performance. FIG. 5 depicts typical S₂₁ measurement resultfor a conventional CLC EMI filter circuit corresponding to aconventional filter shown in FIG. 3. It supports a pass-band of aboutf_(c)=320 MHz wide, good for high data rates up to 120 Mbps. However,the rejection-band attenuation at 800 MHz is only about −23 dB, which isless than the desired −30 dB target.

In view of the problems and shortcomings of the prior art, the presentinvention provides an integrated circuit (IC) electromagneticinterference (EMI) filter with electrostatic discharge (ESD) protectionincorporating inductor-capacitor (LC) resonance tanks, so as to solvethe afore-mentioned problems of the prior art.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide an integratedcircuit (IC) electromagnetic interference (EMI) filter, which uses ahigh-order resonating LC tank method and integrates an ElectromagneticDisturbance (EMI) filter in the integrated circuit (IC) format with therequired ESD protection components on a chip or within one package toachieve excellent filter circuit performance.

To achieve the abovementioned objectives, the present invention proposesan IC EMI filter with ESD protection incorporating LC resonance tanks.The filter comprises a first diode with a first anode thereof coupled tothe ground, and the first diode induces a first parasitic capacitancebetween a first cathode of the first diode and the first anode. Thefirst cathode is coupled to a first inductor having a first seriesresistance. The ground is coupled to a second anode of a second diode.The second diode induces a second parasitic capacitance between a secondcathode of the second diode and the second anode. The second cathode iscoupled to a second inductor having a second series resistance. A firstpassive element is coupled between the first and second inductors. Afirst node between the first passive element and the first inductor iscoupled to a first port. A second node between the first passive elementand the second inductor is coupled to a second port. The first inductor,the second inductor, and the first passive element induce a thirdparasitic capacitance between the first node and the first anode and afourth parasitic capacitance between the second node and the secondanode.

The present invention proposes another IC EMI filter with ESDprotection. The filter comprises a first diode with a first anodethereof coupled to the ground, and the first diode induces a firstparasitic capacitance between a first cathode of the first diode and thefirst anode. The first cathode is coupled to an inductor having a seriesresistance. The ground is coupled to a second anode of a second diode.The second diode induces a second parasitic capacitance between a secondcathode of the second diode and the second anode. The second cathode iscoupled to a first port. There is a first passive element coupledbetween the second cathode and the inductor. The ground is coupled to athird anode of a third diode. The third diode induces a third parasiticcapacitance between a third cathode of the third diode and the thirdanode. The third cathode is coupled to a second port. There is a secondpassive element coupled between the third cathode and the inductor andcooperating with the first passive element and the inductor to induce afourth parasitic capacitance between the first anode and a node amongthe first passive element, the second passive element, and the inductor.

Below, the embodiments are described in detailed in cooperation with theattached drawings to make easily understood the technical contents,characteristics, and accomplishments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a diagram schematically showing a traditional CLC typelow-pass-filter (LPF) circuit;

FIG. 1( b) is a diagram schematically showing a traditional CRC type LPFcircuit;

FIG. 2 is a diagram showing the typical filter insertion loss curve of atraditional LPF;

FIG. 3 is a diagram schematically showing a traditional CLC type LPFcircuit with integrated electrostatic discharge (ESD) protection diodesin real designs;

FIG. 4 is a sample application diagram schematically showing atraditional Electromagnetic Disturbance (EMI) filter;

FIG. 5 is a diagram showing the typical filter insertion loss curve ofthe CLC type LPF shown in FIG. 3;

FIG. 6( a) is a diagram schematically showing a CLC type LPF circuitusing two L-C tanks at input and output ports according to an embodimentof the present invention;

FIG. 6( b) is a diagram schematically showing a CLC type LPF circuitusing two L-C-C tanks at input and output ports according to anembodiment of the present invention;

FIG. 7 is a diagram schematically showing a CLC type LPF circuitaccording to the first embodiment of the present invention;

FIG. 8 is a diagram showing the insertion loss curve comparison for theCLC type LPFs shown in FIG. 3 and FIG. 7 according to an embodiment ofthe present invention;

FIG. 9 is a diagram schematically showing a CLC type LPF circuitaccording to the second embodiment of the present invention;

FIG. 10 is a diagram showing the insertion loss curve comparison for theCLC type LPFs shown in FIG. 3 and FIG. 9 according to an embodiment ofthe present invention;

FIG. 11 is a diagram schematically showing a CLC type LPF circuitaccording to the third embodiment of the present invention;

FIG. 12 is a diagram showing the insertion loss curve comparison for theCLC type LPFs shown in FIG. 9 and FIG. 11 according to an embodiment ofthe present invention;

FIG. 13 is a diagram schematically showing a CRC type LPF circuitaccording to the fourth embodiment of the present invention;

FIG. 14 is a diagram schematically showing a CRC type LPF circuitaccording to the fifth embodiment of the present invention; and

FIG. 15 is a diagram schematically showing a CRC type LPF circuitaccording to the sixth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the first embodiment, the present invention aims to improve theconventional CLC type filter shown in FIG. 3, which is depicted in FIG.6 for its conceptual circuitry. The new filter circuit utilizes aspecial LC resonance tank at both signal input and output nodes of theconventional 2-port CLC filter circuit to improve the rejection bandattenuation though careful frequency compensation. In one exampleschematic shown in FIG. 6( a), a new L-C tank consisting of an inductor34 and a capacitor 36 is connected between Node-3 and Node-5, while anew L-C tank consisting of an inductor 38 and a capacitor 40 isconnected between Node-4 and Node-5. Alternatively, FIG. 6( b)illustrates a similar new circuit using a first L-C-C tank and a secondL-C-C tank at the input and output ports of the CLC LPF circuit,respectively. The first L-C-C tank consists of an inductor 42 and twocapacitors 44 and 46, and the second L-C-C tank consists of an inductor48 and two capacitors 50 and 52. Through accurate frequency compensationusing the integrated LC tanks, the rejection band attenuation can besignificantly improved by carefully design of the LC resonant frequencyof the new circuit.

Refer to FIG. 7. The first embodiment of the present invention isdescribed as below. The present invention comprises a first diode 54.The first diode 54 can induce a first parasitic capacitance 56 betweenthe first cathode and the first anode of the first diode 54. The firstcathode is coupled to a first inductor 58 having a first seriesresistance 60. A second diode 62 can induce a second parasiticcapacitance 64 coupled between the second cathode and the second anodeof the second diode 62. The second cathode is coupled to a secondinductor 66 having a second series resistance 68. The first and secondanodes are coupled to the ground through a parasitic resistance 691 anda first parasitic inductor 692 connected in series and associated withbonding and package of the filter. A first passive element is coupledbetween the first and second inductors 58 and 66. In the firstembodiment, the first passive element is exemplified by an inductor 70with a series resistance 72. A first node is placed between the inductor70 and the first inductor 58, and a second node is placed between theinductor 70 and the second inductor 66. The first inductor 58, thesecond inductor 66, and the inductor 70 can induce a third parasiticcapacitance 74 between the first node and the first anode and a fourthparasitic capacitance 76 between the second node and the second anode.Besides, the first node is coupled to a first port through a secondparasitic inductor 80 associated with bonding and package of the filter;and the second node is coupled to a second port through a thirdparasitic inductor 82 associated with bonding and package of the filter.

FIG. 8 gives the insertion loss S₂₁ curves for two typical LPF circuitsin FIG. 3 and FIG. 7, which clearly shows the significant improvement inall critical specs by using the new circuit technique in the presentinvention. Specifically, the rejection-band attenuation is enhanced to−30 dB while keeping f_(c)=320 MHz for broad pass-band. In actualdesign, the values for the first parasitic capacitance 56, the firstinductor 58, the third parasitic capacitance 74, the second parasiticcapacitance 64, the second inductor 66 and the parasitic resistance 76,etc., ought to be selected rationally to purposely create the requiredfrequency resonant points, as observed in FIG. 8, which serves toachieve a wider high-attenuation rejection bandwidth with sharp roll-offcurve as desired.

Refer to FIG. 9. The second embodiment of the present invention isdescribed as below. The present invention comprises a first diode 84.The first diode 84 can induce a first parasitic capacitance 86 betweenthe first cathode and the first anode of the first diode 84. The firstcathode is coupled to an inductor 88 having a series resistance 90. Asecond diode 92 can induce a second parasitic capacitance 94 between thesecond cathode and the second anode of the second diode 92. The secondcathode is coupled to a first port through a second parasitic inductor96 associated with bonding and package of the filter. A first passiveelement is coupled between the second cathode and the inductor 88. Inthe second embodiment, the first passive element is exemplified by aninductor 98 with a series resistance 100. A third diode 102 can induce athird parasitic capacitance 104 between the third cathode and the thirdanode of the third diode 102. The third cathode is coupled to a secondport through a third parasitic inductor 106 associated with bonding andpackage of the filter. The first, second and third anodes are coupled tothe ground through a parasitic resistance 108 and a first parasiticinductor 110 connected in series and associated with bonding and packageof the filter. A second passive element is coupled between the thirdcathode and the inductor 88 and cooperates with the inductor 98 and theinductor 88 to induce a fourth parasitic capacitance 112 between thefirst anode and a node among the second passive element, and theinductors 88 and 98. In the second embodiment, the second passiveelement is exemplified by an inductor 114 with a series resistance 116.

FIG. 10 shows that the rejection-band attenuation performance of thisnew LPF filter circuit improves significantly over the conventionalcircuit, i.e., f_(c)=328 MHz, a steeper roll-off curve from thepass-band to the rejection-band and much higher rejection-bandattenuation (−33 dB @ 800 MHz vs. −23 dB @ 800 MHz, −47 dB @ 1 GHz vs.−28 dB @ 1 GHz, and −48 dB @ 2 GHz vs. −40 dB @ 2 GHz). Meanwhile, thesecond embodiment schematic helps to prevent possible inductor inducedovershot in the voltage clamping voltage during ESD stressing.

Refer to FIG. 11. The third embodiment of the present invention isdescribed as below. The present invention comprises a first diode 54.The first diode 54 can induce a first parasitic capacitance 56 betweenthe first cathode and the first anode of the first diode 54. The firstcathode is coupled to a first inductor 58 having a first seriesresistance 60. A second diode 62 can induce a second parasiticcapacitance 64 coupled between the second cathode and the second anodeof the second diode 62. The second cathode is coupled to a secondinductor 66 having a second series resistance 68. A first passiveelement is coupled between the first and second inductors 58 and 66. Inthe third embodiment, the first passive element is exemplified by aninductor 70 with a series resistance 72. A first node is placed betweenthe inductor 70 and the first inductor 58, and a second node is placedbetween the inductor 70 and the second inductor 66.

A second passive element has two ends. One end is coupled to the firstnode, and another end is coupled to a second parasitic inductor 118associated with bonding and package of the filter and a first port inorder. The second passive element is coupled between the first node andthe second parasitic inductor 118. The second passive element isexemplified by an inductor 120 with a series resistance 122. The thirdcathode of a third diode 124 is coupled to a third node between thesecond parasitic inductor 118 and the inductor 120, and the third diode124 can induce a fifth parasitic capacitance 126 between the thirdcathode and the third anode of the third diode 124. A third passiveelement has two ends. One end is coupled to the second node, and anotherend is coupled to a third parasitic inductor 128 associated with bondingand package of the filter and a second port in order. The third passiveelement is coupled between the second node and the third parasiticinductor 128 and cooperates with the first inductor 58, the secondinductor 66, the inductors 70 and 120 to induce a third parasiticcapacitance 130 between the first node and the first anode and a fourthparasitic capacitance 132 between the second node and the second anode.The third passive element is exemplified by an inductor 134 with aseries resistance 136. The fourth cathode of a fourth diode 138 iscoupled to a fourth node between the third parasitic inductor 128 andthe inductor 134. The fourth diode 138 can induce a sixth parasiticcapacitance 140 between the fourth cathode and the fourth anode.Besides, the first, second, third, and fourth anodes are coupled to theground through a parasitic resistance 142 and a first parasitic inductor144 connected in series and associated with bonding and package of thefilter.

In the third embodiment, the invention results in new higher-order LPFfilter circuit schematics utilizing several parallel frequency resonantLC tanks in a distributed network format. FIG. 11 illustrates one ofsuch high-order LPF filter with two LC resonance tanks originated fromthat in FIG. 9. Such higher-order distributed LC resonance tank basedLPF circuit allows very fine-tune in frequency compensation andtherefore can further improve the RF filter performance including thecritical rejection-band attenuation. FIG. 12 gives the S₂₁ curvecomparison of the new filter circuit shown in FIG. 11 and the oneillustrated in FIG. 9, which clearly shows RF performance improvement,particularly the much steeper roll-off rate to excellent rejection band.

In addition to the CLC LPF filters discussed previously, the new circuittechniques can be easily applied to any CRC type LPF circuits as well.Furthermore, they can be readily applied to any combined CLC and CRCmixed type filter circuits. For example, FIG. 13 is the fourthembodiment of the present invention. The fourth embodiment is differentfrom the first embodiment in the first passive element. In the fourthembodiment, the first element is exemplified by a resistor 146. Thefirst inductor 58, the second inductor 66, and the resistor 146 caninduce a third parasitic capacitance 74 and a fourth parasiticcapacitance 76. In addition, FIG. 14 and FIG. 15 are respectively thefifth and sixth embodiments of the present invention. By the same token,the fifth embodiment is different from the second embodiment in thefirst and second passive elements. In the fifth embodiment, the firstand second elements are respectively exemplified by resistors 148 and150. The resistors 148 and 150 and the inductor 88 can induce a fourthparasitic capacitance 112. The sixth embodiment is different from thethird embodiment in the first, second and third passive elements. In thesixth embodiment, the first, second and third elements are respectivelyexemplified by resistors 152, 154 and 156. The resistors 152, 154 and156, the first inductor 58, and the second inductor 66 can induce athird parasitic capacitance 130 and a fourth parasitic capacitance 132.These new CRC filter circuits utilizing the new resonant LC tanktechnique achieves superior rejection-band RF performance over itsconventional counterpart.

In conclusion, the present invention uses the LC tank method to achieveexcellent filter circuit performance.

The embodiments described above are only to exemplify the presentinvention but not to limit the scope of the present invention.Therefore, any equivalent modification or variation according to theshapes, structures, characteristics and spirit of the present inventionis to be also included within the scope of the present invention.

1. An integrated circuit (IC) electromagnetic interference (EMI) filterwith electrostatic discharge (ESD) protection incorporatinginductor-capacitor (LC) resonance tanks, said IC EMI filter comprising:a first diode with a first anode thereof coupled to a ground, whereinsaid first diode comprises a first parasitic capacitance between a firstcathode of said first diode and said first anode; a first inductorhaving a first series resistance, and being coupled to said firstcathode; a second diode with a second anode thereof coupled to saidground, wherein said second diode comprises a second parasiticcapacitance between a second cathode of said second diode and saidsecond anode; a second inductor having a second series resistance, andbeing coupled to said second cathode; and a first passive elementcoupled between said first and second inductors, wherein a first nodebetween said first passive element and said first inductor is coupled toa first port, and a second node between said first passive element andsaid second inductor is coupled to a second port.
 2. The IC EMI filterof claim 1, wherein: said first and second anodes are coupled to saidground through a parasitic resistance and a first parasitic inductorthat are associated with bonding and package; said first node is coupledto said first port through a second parasitic inductor that isassociated with said bonding and package; and said second node iscoupled to said second port through a third parasitic inductor that isassociated with said bonding and package.
 3. The IC EMI filter of claim1, wherein said first passive element comprises at least one of aresistor and an inductor with a series resistance.
 4. The IC EMI filterof claim 1, further comprising: a second passive element coupled betweensaid first node and said first port; a third diode with a third cathodethereof coupled to a third node between said first port and said secondpassive element, and a third anode thereof coupled to said ground,wherein said third diode comprises a fifth parasitic capacitance betweensaid third cathode and said third anode; a third passive element coupledbetween said second node and said second port and cooperating with saidfirst and second inductors and said first and second passive elements toinduce third and fourth parasitic capacitances; and a fourth diode witha fourth cathode thereof coupled to a fourth node between said secondport and said third passive element, and a fourth anode thereof coupledto said ground, wherein said fourth diode comprises a sixth parasiticcapacitance between said fourth cathode and said fourth anode.
 5. The ICEMI filter of claim 4, wherein: said first, second, third, and fourthanodes are coupled to said ground through a parasitic resistance and afirst parasitic inductor that are associated with bonding and package;said third node is coupled to said first port through a second parasiticinductor that is associated with said bonding and package; and saidfourth node is coupled to said second port through a third parasiticinductor that is associated with said bonding and package.
 6. The IC EMIfilter of claim 4, wherein each of said second and third passiveelements comprises an inductor with a series resistance.
 7. The IC EMIfilter of claim 4, wherein each of said second and third passiveelements comprises a resistor element is a resistor.
 8. An integratedcircuit (IC) electromagnetic interference (EMI) filter withelectrostatic discharge (ESD) protection incorporatinginductor-capacitor (LC) resonance tanks, said IC EMI filter comprising:a first diode with a first anode thereof coupled to a ground, whereinsaid first diode comprises a first parasitic capacitance between a firstcathode of said first diode and said first anode; an inductor having aseries resistance, and being coupled to said first cathode; a seconddiode with a second anode thereof coupled to said ground, wherein saidsecond diode comprises a second parasitic capacitance between a secondcathode of said second diode and said second anode, and wherein saidsecond cathode is coupled to a first port; a first passive elementcoupled between said second cathode and said inductor; a third diodewith a third anode thereof coupled to said ground, wherein said thirddiode comprises a third parasitic capacitance between a third cathode ofsaid third diode and said third anode, and wherein said third cathode iscoupled to a second port; and a second passive element coupled betweensaid third cathode and said inductor.
 9. The IC EMI filter of claim 8,wherein: said first, second and third anodes are coupled to said groundthrough a parasitic resistance and a first parasitic inductor that areassociated with bonding and package; said second cathode is coupled tosaid first port through a second parasitic inductor that is associatedwith said bonding and package; and said third cathode is coupled to saidsecond port through a third parasitic inductor that is associated withsaid bonding and package.
 10. The IC EMI filter of claim 8, wherein eachof said first and second passive elements comprises an inductor with aseries resistance.
 11. The IC EMI filter of claim 8, wherein each ofsaid first and second passive elements comprises a resistor.